New antimicrobial peptides, their variants and uses

ABSTRACT

The present invention relates to novel antimicrobial peptide and variants thereof. The invention further relates to method of killing or inhibiting growth of microbes and use of the peptide here disclosed as a medicament, feed additive, preservative or surfactant.

FIELD OF INVENTION

The present invention relates to antimicrobial peptides or variants thereof, to a method of killing or inhibiting growth of microbes and to a use of the peptide described here as a medicament, feed additive, preservative or surfactant.

BACKGROUND

Among drug compounds, antibiotics have had a tremendous impact on the life expectancy of mankind. However, the capacity of microbes to develop resistance is almost unlimited. Multi-drug resistance has become a very common and dangerous characteristic of many human pathogens, and drug resistance is spreading across the globe.

Endophytes are promising producers of a wide array of secondary metabolites with potential application in biomedicine, pharmaceutical and healthcare industries. The methodology typically used for studying functional diversity of endophytes is based on isolation with an emphasis towards fast-growing strains, thus not representing the full biodiversity. Methods such as denaturing gradient gel electrophoresis (DGGE), restriction fragment length polymorphism (RFLP) or cloning and direct sequencing are used for analyzing the diversity of unculturable fungal communities in plants, but such methods are not suitable for the functional studies. A frequent problem with endophytes is that they produce metabolites only for a certain period of time in vitro and then become inactive, lose viability or ability to produce bioactive secondary metabolites. Such culturing problems on other microbes have earlier been one of the driving forces for development of new methods to access the vast microbial wealth.

Antimicrobial peptides (AMPs) are evolutionarily conserved and produced by innate immune system in all complex organisms. They serve as the first line of defense in humans and mammals. AMPs are polypeptides composed of 10-50 amino acids with ≥30% of hydrophobic ratios and positive charge. In general, AMPs have broadspectrum antimicrobial activity against bacteria, fungi and yeast. WO 2011/113999 discloses tryptic polypeptides from endophyte of Empetrum nigrum and methods for obtaining them. Based on in silico analysis the peptides are predicted to have antimicrobial activity.

There is an urgent need for new molecules having activity against various pathogenic microbes. This invention meets these needs as explained in the following.

SUMMARY OF THE INVENTION

Crowberry (Empetrum nigrum) is a perennial shrub growing in the northern hemisphere that has traditionally been used for treating infectious diseases and was considered a good candidate for such studies. The present invention provides novel antimicrobial (poly) peptides derived from an endophyte of E. nigrum and variants thereof having improved activity against various microbes.

The first aspect of the invention is to provide an antimicrobial peptide or a variant thereof. According to the invention said polypeptide comprises SEQ ID NO: 5 or has at least 37% identity to SEQ ID NO: 5.

The second aspect of the invention is a method of killing or inhibiting growth of microbes. According to the invention said method comprises a step of treating said microbes with a peptide or a variant thereof here described.

The third aspect of the invention is a use of the peptide or a variant thereof here described as a medicament, feed additive, preservative or surfactant.

Considerable advantages are obtained by the invention. The AMPs are known to be active against broad spectrum of microbes, including fungi and both Gram positive and Gram negative bacteria. Small AMPs are easy to synthesize and commercially viable as the cost of production is minimal. AMPs are not known to develop resistance in bacteria. The present invention relates to novel antimicrobial peptides, their variants and use in various applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. An agar-overlay assay showing subclones with antibacterial activity (a) and subclones without activity (s) towards S. aureus, identified in the E. coli-based endophytic metagenomic library.

FIG. 2. Predicted amino acid sequence of Empetrum nigrum metagenomic antibacterial protein 1. The predicted protein has 549 residues. Highly conserved PPR-sequences (pentatricopeptide repeats) are underlined.

FIG. 3. The representative Radial Diffusion assay (RDA) of synthesized peptides Met1-Met12, 100 μg each, tested against E. coli (A) and S. aureus (B) NC=negative control, Gentamicin 10 μg.

FIG. 4a shows an alignment of 25 variants of “Met10”-peptide (Chain 100) defined by SEQ ID NO: 4.

FIG. 4b shows an alignment of 23 variants of “Met11”-peptide (Chain 200) defined by SEQ ID NO: 5.

FIG. 4c shows an alignment of 25 variants of “Met12”-peptide (Chain 300) defined by SEQ ID NO: 6.

FIG. 5a shows an alignment of 9 variants of “Met10”-peptide (Chain 100) defined by SEQ ID NO: 4.

FIG. 5b shows an alignment of 10 variants of “Met11”-peptide (Chain 200) defined by SEQ ID NO: 5.

FIG. 5c shows an alignment of 13 variants of “Met12”-peptide (Chain 300) defined by SEQ ID NO: 6.

FIG. 6a . Radial Diffusion assay (RDA) of synthesized peptide variants Chain 100-109, 50 μg each, tested against Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 25923), Klebsiella pneumoniae (ATCC 10031) and Pseudomonas aeruginosa (ATCC 27853), NC=negative control, Gentamicin 5 μg

FIG. 6b . Radial Diffusion assay (RDA) of synthesized peptide variants Chain 200-210, 50 μg each, tested against Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 25923), Klebsiella pneumoniae (ATCC 10031) and Pseudomonas aeruginosa (ATCC 27853), NC=negative control, Gentamicin 5 μg

FIG. 6c . Radial Diffusion assay (RDA) of synthesized peptide variants Chains 300-313, 50 μg each, tested against Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 25923), Klebsiella pneumoniae (ATCC 10031) and Pseudomonas aeruginosa (ATCC 27853), NC=negative control, Gentamicin 5 μg

FIG. 7a . Radial Diffusion assay (RDA) of synthesized peptide variants Chains 109, 105, 104, 201, 204, 310, 308, 307 and 306, 20 μg each, tested against Aspergillus flavus (DSM 1959), NC=negative control, Amphotericin B 20 μg.

FIG. 7b . Radial Diffusion assay (RDA) of synthesized peptide variants chains 109, 105, 104, 201, 204, 310, 308, 307 and 306, 20 μg each, tested against Penicillium chrysogenum (DSM 1075), NC=negative control, Amphotericin B 20 μg.

FIG. 8a . Thermostability of the chain peptides 104 (A-D) and 105 (E-H) tested at various temperatures over a period of 14 days by radial diffusion assay. Antibacterial activity was tested by aliquoting 20 μg of peptides incubated at different temperature and activity was measured by zone of inhibition. Peptides at −20° C. served as control.

FIG. 8b . Thermostability of the chain peptides 201 (A-D) and 204 (E-H) tested at various temperatures over a period of 14 days by radial diffusion assay. Antibacterial activity was tested by aliquoting 20 μg of peptides incubated at different temperature and activity was measured by zone of inhibition. Peptides at −20° C. served as control.

FIG. 8c . Thermostability of the chain peptides 306 (A-D) and 308 (E-H) tested at various temperatures over a period of 14 days by radial diffusion assay. Antibacterial activity was tested by aliquoting 20 μg of peptides incubated at different temperature and activity was measured by zone of inhibition. Peptides at −20° C. served as control.

FIG. 9a . pH stability of chain peptides 104 and 105 was determined by radial diffusion assay (RDA). Different pH ranging from 4-9 was used to check the zone of inhibition.

FIG. 9b . pH stability of chain peptides 201 and 204 was determined by radial diffusion assay (RDA). Different pH ranging from 4-9 was used to check the zone of inhibition.

FIG. 9c . pH stability of chain peptides 306 and 308 was determined by radial diffusion assay (RDA). Different pH ranging from 4-9 was used to check the zone of inhibition.

FIG. 10c . Narrow spectrum antimicrobial activity of chain peptide 306.

FIG. 11a . Transmission electron microscopy (TEM) image of E. coli (A-C) and S. aureus (D-G) exposed to 10 μg/ml of chain 105 at 37° C. for 1 h. Control (A & D); Treated with chain 105 (B-C & E-G).

FIG. 11b . Transmission electron microscopy (TEM) image of E. coli (A-C) and S. aureus (D-F) exposed to 10 μg/ml of chain 201 at 37° C. for 1 h. Control (A & D); Treated with chain 201 (B-C & E-F).

FIG. 11c . Transmission electron microscopy (TEM) image of E. coli (A-C) and S. aureus (D-F) exposed to 10 μg/ml of chain 308 at 37° C. for 1 h. Control (A & D); Treated with chain 308 (B-C & E-F).

FIG. 12. Antibacterial activity of Chain 105 and 201 immobilized catheters. Silicon catheters were used as controls.

DETAILED DESCRIPTION

Endophytes, microorganisms which spend their entire life cycle, or parts of it, inside of healthy tissues of a host plant, are found in all plant species. Whereas the majority of endophytes cannot be cultured, it is not surprising that a chemical structure isolated from a plant can actually have a microbial origin. Metagenomics provides a valuable tool to access the resources of bioactive compounds derived from unculturable microorganisms.

In this study, we have constructed a metagenomic library from endophytes and screened for antibacterial activity. The library was screened to select antimicrobial clones using Staphylococcus aureus as a target organism by the double-agar-layer method. One unique clone exhibiting antibacterial activity was selected from the metagenomic library. Secondary libraries were generated to obtain antibacterial subclones with reduced insert size for characterization of the gene responsible for the antibacterial activity.

The nucleotide sequence of the subclone was subjected to BLAST analyses against sequences present in the Genbank databases but no similarity to any known sequence was identified. The isolated gene encoded for a protein disclosed is in WO 2011/113999 and named as Empetrum nigrum metagenomic antibacterial protein 1 (En-MAP1, GenBank accession number KC466596). Analysis of the deduced amino acid sequence (SEQ D NO: 1) revealed that En-MAP1 encodes for a protein of 549 amino acids sharing the highest similarity of 32% to a hypothetical protein from Pseudozyma hubeiensis and no similarity to any protein of known function.

The isolated endophytic protein was expressed and isolated but no antimicrobial activity was observed. Antimicrobial activity of the in silico digested peptides was then predicted using algorithms described in the experimental part. The peptides were also tested for antimicrobial activity against S. aureus, E. coli and Verticillium dahliae. In preliminary tests some of the peptides predicted to have antimicrobial activity showed activity also in in vitro tests. Best candidates were selected for further studies.

Antimicrobial peptides interact with bacterial membranes to efficiently kill at optimum concentration. AMPs should also possess biocompatibility, salt tolerance and broad spectrum antimicrobial activity. By using rational design techniques, we were able to improve the peptide antimicrobial activity by incorporating or replacing various amino acids. We have designed and modified Met10 (Chain 100 defined by SEQ ID NO: 4), Met11 (Chain 200 defined by SEQ ID NO: 5), and Met12 (Chain 300 defined by SEQ ID NO: 6), peptides with tryptophan (W), arginine (R) and lysine (K) at various positions to improve antibacterial activity.

APD2 database was utilized to check the homology and identities of the peptides to known antimicrobials (Wang et al., 2009).

An embodiment of the invention is an antimicrobial peptide or a variant thereof comprising SEQ ID NO: 4 (Met 10, chain 100), SEQ ID NO: 5 (Met11, chain 200), SEQ ID NO: 6 (Met12, chain 300), or having at least 37% identity to SEQ ID NO: SEQ ID NO: 4, SEQ ID NO: 5 or SEQ ID NO: 6. It has surprisingly been found that relatively small fragments may have desired activity.

In one embodiment the peptide or a variant thereof comprises any of SEQ ID NO: 4, SEQ ID NO: 5 or SEQ ID NO: 6 or a peptide having at least 40%, preferably at least 50%, 60%, 70% identity to any of said sequences, more preferably at least 80% identity to any of said sequences and most preferably 90% or even 95% identity to said SEQ ID NO: 4, SEQ ID NO: 5 or SEQ ID NO: 6.

In this connection the term “identity” refers to the global identity between two amino acid sequences compared to each other from the first amino acid to the last corresponding amino acid. Thus a fragment can only be compared to respective amino acids (essentially equal number of amino acids) of the mature (poly) peptide.

In one embodiment of the invention the peptide comprising any of SEQ ID NO: 4, SEQ ID NO: 5 and SEQ ID NO: 6 is modified in order to increase antimicrobial activity.

According to one embodiment the peptide is modified with one or more of W, R, K, L, C, I, F and A-substitutions, more preferably with one or more of W, R and A-substitutions. These substitutions increase the interaction with microbial membranes and thereby improve antimicrobial activity.

In one embodiment the peptide defined by SEQ ID NO: 4 (chain 100) comprises one or more, preferably, five, six or even seven substitutions selected from the group consisting of V16K/L/W/R; Q15R/L/W/I/F/C; N14L/K/R/W; /W; A11W; M6W and I7W.

Preferably amino acid residues R8, L9 and H10 of SEQ ID NO: 4 are not modified.

According to one embodiment the peptide comprises one or more substitutions or deletions in SEQ ID NO: 4 (chain 100) selected from the group consisting of

-   -   a. D1-/R     -   b. C2-/K     -   c. W3-     -   d. S4-/R     -   e. A5-     -   f. M6W     -   g. I7W     -   h. A11W     -   i. Y13W/R     -   j. N14L/K     -   k. Q15R/L     -   l. V16K/W         wherein “-” indicates deletion of the amino acid.

In one embodiment of the invention the peptide when compared to the original peptide defined by SEQ ID NO: 4 (chain 100), has 1 to 5, preferably 5 N-terminal amino acids been deleted. It has been found that the shorter peptides are able to maintain their antimicrobial activity. In addition shorter peptides result in lower cost of synthesis.

In a further embodiment the peptide variant of SEQ ID NO: 4 with N-terminal deletion further comprises one, two, three, four, five, six, seven or all amino acid modifications selected from the group consisting of V16K/W; Q15R/L; N14L/K; Y13R/W; A11W; I7W and M6W.

According to one embodiment the peptide defined by SEQ ID NO: 5 is modified with one or more of W, R, K, F, I and L-substitutions, more preferably with one or more of W, K and R-substitutions. These substitutions increase the interaction with microbial membranes and thereby improve antimicrobial activity.

In one embodiment the peptide defined by SEQ ID NO: 5 (chain 200) comprises one or more, preferably at least six, seven, eight, nine or even 10 substitutions selected from the group consisting of N1R/K/W, R2W, I3L, V4/I/L, Q5W/K/R, Q6R/L/W, R7W, T8R/W/F, S9F/W/R/L and S10K/L.

Alternatively or in addition the peptide defined by SEQ ID NO: 5 can be modified by C-terminal addition of K (for example chain 207 defined by SEQ ID NO: 15) In one embodiment amino acid residue R11 of peptide defined by SEQ ID NO: 5 is not modified.

According to one embodiment the peptide comprises one or more substitutions or deletions in SEQ ID NO: 5 (chain 200) selected from the group consisting of

-   -   a. N1K/R/W     -   b. R2W     -   c. I3L     -   d. V41/L     -   e. Q5W/K/R     -   f. Q6R/L/W     -   g. R7W/R     -   h. T8R/W/F/K     -   i. S9F/W/R/L     -   j. S10K/L

According to one embodiment the peptide defined by SEQ ID NO: 6 is modified with one or more of W, R, K, L, and I-substitutions, more preferably with one or more of W and R-substitutions. These substitutions increase the interaction with microbial membranes and thereby improve antimicrobial activity.

In one embodiment the peptide defined by SEQ ID NO: 6 (chain 300) comprises one or more, preferably four, five, six, seven, eight or even nine substitutions selected from the group consisting of Y1I/R/W/K, D2I/L/W/R, G4R/W, F5W/R, G6R/W/L, F8R, K9R, K10R and M11L/R/W/K.

Preferably amino acid residues K3 and L7 of the peptide defined by SEQ ID NO: 6 are not modified.

Alternatively or in addition the peptide defined by SEQ ID NO: 6 can be modified by addition of K between amino acid residues 9 and 10 (for example chain 313 defined by SEQ ID NO: 32).

According to one embodiment the peptide comprises one or more substitutions or deletions in SEQ ID NO: 6 (chain 300) selected from the group consisting of

-   -   a. Y1I/R/W/K     -   b. D2I/L/W/R     -   d. G4R/W     -   e. F5W/R     -   f. G6R/W/L     -   h. F8R     -   i. K9R     -   j. K10R     -   k. M11L/R/W/K.

In an embodiment the peptide or a variant thereof comprises a sequence selected from SEQ ID NO: 4 (chain 100) or one of SEQ ID NOs 7 to 31 (chains 101 to 125) or consists of it.

In an embodiment the peptide variant (peptide) comprises a sequence selected from SEQ ID NOs 7 to 15 (chains 101 to 109) or consists of it. In an embodiment the peptide variant comprises a sequence selected from SEQ ID NOs 10 to 15 (chains 104 to 109) or consists of it. In an embodiment the peptide variant comprises a sequence selected from SEQ ID NOs 10, 11 and 15 (chains 104, 105 and 109) or consists of it.

In an embodiment the peptide comprises SEQ ID NO: 4 (chain 100). In an embodiment the peptide consists of SEQ ID NO: 4 (chain 100).

In an embodiment the peptide or a variant thereof comprises a sequence selected from SEQ ID NO: 5 (chain 200) or one of SEQ ID NOs 32 to 54 (chains 201 to 223) or consists of it.

In an embodiment the peptide variant comprises a sequence selected from SEQ ID NOs 32 to 41 (chains 201 to 210) or consist of it. In an embodiment the peptide variant comprises a sequence selected from SEQ ID NOs 32, 34, 35 and 39 (chains 201, 203, 204 or 208) or consists of it.

In an embodiment the peptide comprises SEQ ID NO: 5 (chain 200). In an embodiment the peptide consists of SEQ ID NO: 5 (chain 200).

In an embodiment the peptide or a variant thereof comprises a sequence selected from SEQ ID NO: 6 (chain 300) or one of SEQ ID NOs 55 to 79 (chains 301 to 325) or consists of it.

In an embodiment the peptide variant comprises a sequence selected from SEQ ID NOs 55 to 67 (chains 301 to 313) or consists of it. In an embodiment the peptide variant comprises a sequence selected from SEQ ID NOs 55, 58, 59 and 61 to 65 (chains 301, 304, 305 or 307 to 311) or consists of it.

In an embodiment the peptide variant comprises a sequence selected from SEQ ID NOs 61 and 62 (chains 307 and 308) or consists of it.

In an embodiment the peptide comprises SEQ ID NO: 6 (chain 300). In an embodiment the peptide consists of SEQ ID NO: 6 (chain 300).

It is evident that peptides and their variants have different antimicrobial activities against different microbes. In this study antimicrobial activity was tested against both bacteria and fungi.

Antibacterial activity of selected peptides (peptide variants) was tested against Escherichia coli (ATCC 25922), Klebsiella pneumoniae (ATCC 10031), Pseudomonas aeruginosa (ATCC 27853) and Staphylococcus aureus (ATCC 25923). Radial diffusion assay and minimum inhibitory concentration was used to determine the antibacterial activity, where radial diffusion assay was used to asses the antifungal activity of the peptide variants.

Antifungal activity was tested against Aspergillus flavus (DSM 1959) and Penicillium chrysogenum (DSM 1075).

In an embodiment the peptide or a fragment thereof is chemically synthesized (synthetic peptide). In another embodiment the peptide has been recombinantly produced. In one embodiment the peptide or peptides are isolated from the growth medium of recombinant peptide production or synthesis medium.

In one embodiment, the antimicrobial peptide is attached to a surface of a medical device, food package, carrier substance or e.g. biosensor, optionally using a linker peptide. Alternatively or in addition, in another embodiment the peptide is attached to detectable agents such as for example fluorescent agent or an enzyme substrate for example when using the antimicrobial peptide in biosensors. In one embodiment, said peptides are immobilized on silicon, polyethene, and other materials in order to be used as medicine or coating agents.

In hemolysis assays, the ability of peptides at 128 μg/ml concentration to lyse human erythrocytes to release hemoglobin was measured. The peptides described here preferably have low hemolytic activity (0.2 to 3.8% hemolysis) in mammal body. The hemolytic concentration tested (128 μg/ml) is more than 50 fold of minimal inhibitory concentration (MIC) of chains 105, 201 and 308 and hemolysis is negligible at 0.2-0.5% respectively. These peptides are useful as antimicrobial drugs as they show little or no side effects at concentrations needed to kill bacteria.

In one embodiment the peptide or a variant thereof exhibits an activity against microorganisms, in particular against gram positive and gram negative bacteria, in particular against the families Staphylococcaceae and Enterobacteriaceae. In one embodiment the peptide exhibits an activity against yeast and/or fungi.

In one embodiment the peptide or a variant thereof exhibits an activity against bacteria. In one embodiment the peptide or a variant thereof exhibits an activity against fungi. In one embodiment the peptide or a variant thereof exhibits an activity against bacteria and fungi. Activity against bacteria and/or fungi can be for example suppression of multiplication or growth of said microbes or killing them.

In one embodiment the peptide or a variant thereof exhibits an activity against gram positive bacteria, in particular microorganisms of the family Staphylococcaceae, in particular against microorganisms of the species S. aureus.

Peptides comprising essentially any of SEQ ID NOs: 10 to 15 (Chains 104 to 109), SEQ ID NOs: 32, 34 to 36, 39 to 41 (Chains 201, 203 to 205, 208 to 210) and SEQ ID NOs: 55 to 65 and 67 (Chains 301 to 311 and 313) are particularly active against Staphylococcaceae, particularly S. aureus. S. aureus has developed resistance to most of the commercially available antibiotics. Antimicrobial peptides as we describe here, are a promising class of new antibiotics, as they do not induce resistance in microorganisms.

In one embodiment the peptide exhibits an activity against gram negative bacteria, in particular against E. coli. Peptides comprising essentially any of SEQ ID NOs: 10 to 15 (Chains 104 to 109), SEQ ID NOs: 32, 34 to 36, 39 to 41 (Chains 201, 203 to 206, 208 to 210) and SEQ ID NOs: 55 to 65 and 67 (Chains 301 to 311 and 313) are particularly active against E. coli.

In one embodiment the peptide exhibits an activity against Klebsiella, particularly Klebsiella pneumoniae. Peptides comprising essentially any of SEQ ID NOs: 10 to 15 (Chains 104 to 109), SEQ ID NOs: 32, 34, 35, 39 to 41 (Chains 201, 203, 204, 208 to 210) and SEQ ID NOs: 55, 58, 59, 61 to 65, and 67 (Chains 301, 304, 305, 307 to 311 to 311 and 313) are particularly active against Klebsiella.

In one embodiment the peptide exhibits an activity against Pseudomonas, particularly Pseudomonas aeruginosa. Peptides comprising essentially any of SEQ ID NOs: 10 to 12 and 15 (Chains 104 to 106, 109), SEQ ID NOs: 32, 34, 35 and 39 (Chains 201, 203, 204, 208) and SEQ ID NOs: 55 to 65 and 67 (Chains 301 to 311 and 313), are particularly active against Pseudomonas.

In one embodiment the peptide exhibits an activity against Aspergilli, particularly A. flavus. Peptides comprising essentially any of SEQ ID NO: 10, 11 or 15, SEQ ID NO: 32 or 35 (Chains 104, 105 or 109), SEQ ID NOs: 32 or 35 (chains 201 or 204); SEQ ID NOs: 60, 61, 62 and 64 (chains 306, 307, 308 and 310) are particularly active against Aspergilli.

In one embodiment the peptide exhibits an activity against Penicillium, particularly P. chrysogenum. Peptides comprising essentially any of SEQ ID NO: 10, 11 or 15, SEQ ID NO: 32 or 35 (Chains 104, 105 or 109), SEQ ID NOs: 32 or 35 (chains 201 or 204); SEQ ID NOs: 60, 61, 62 and 64 (chains 306, 307, 308 and 310) are particularly active against Penicillium.

In one embodiment the peptide exhibits an activity against clinical strains of E. coli, K. pneumoniae, E. cloacae, P. aeruginosa, Serratia marcescens, Proteus mirabilis, S. pneumoniae, Acinetobacter baumannii, A. johnsonii, S. aureus, Candida albicans, C. glabrata, C. parapsilosis and C. quillermondiae. Peptides comprising essentially any of SEQ ID NO: 10, 11 or 15, SEQ ID NO: 32 or 35 (Chains 104, 105 or 109), SEQ ID NOs: 32 or 35 (chains 201 or 204); SEQ ID NOs: 58, 60, 61, 62, 63, 64 and 65 (chains 304, 306, 307, 308, 309, 310 and 311).

Chain 104, chain 105, chain 109, chain 201, chain 204, chain 307, chain 308 and chain 310 are demonstrably broad-spectrum antimicrobial peptides, active against gram positive and negative bacteria in a range of 0.5 to 32 μg/ml and has little side effects to humans as tested by hemolysis assay.

The present invention relates also to an antimicrobial composition comprising an antimicrobial peptide or peptides here described. In an embodiment such composition further comprises a pharmaceutically acceptable carrier and optionally other conventional ingredients.

Peptide having SEQ ID NO: 4 (chain 100), SEQ ID NO: 5 (chain 200), SEQ ID NO: 6 (chain 300) or a variant thereof having at least 37%, preferably at least 40%, 50%, 60%, 70%, more preferably at least 80% and most preferably at least 90% identity to said sequence or any peptide according to the present disclosure for use in therapy, particularly for use as an antimicrobial agent.

The antimicrobial activity can be against bacteria or fungi or bacteria and fungi. The bacteria can be gram positive or gram negative bacteria. In particularly the peptide has activity against microorganisms of the genera Staphylococcus or E. coli or both Staphylococcus and E. coli. Various antimicrobial activities and hemolytic properties of the peptides have been discussed above.

One further embodiment of the invention is a use of the peptide according to the present disclosure as a medicament, feed additive, preservative or surfactant.

In one embodiment a peptide having any of SEQ ID NO: 4, 5 or 6 or a variant thereof having at least 37%, preferably at least 40%, 50%, 60%, 70%, more preferably at least 80% and most preferably at least 90% identity to said sequence or any peptide according to the present disclosure is used as a medicament, especially as a medicament against contaminating microbes including S. aureus discussed above.

The present invention relates also to a use of the peptide(s) and their variants described here as a medicament, feed additive, preservative or surfactant is claimed. The toxins produced by various microorganisms contaminate human foods and animal feeds and these peptides used as preservatives may reduce the growth of the contaminants. The activities and other properties of the peptides have been discussed above in connection of other embodiments.

Peptides chain 104, chain 105, chain 109, chain 201, chain 204, chain 307, chain 308 and chain 310 are demonstrably broad-spectrum antimicrobial peptides, active against gram positive and negative bacteria in a range of 0.5 to 32 μg/ml and has little side effects to humans as tested by hemolysis assay. These peptides has a potential for treatment against gram negative infections caused by Escherichia coli (ATCC 25922), Klebsiella pneumoniae (ATCC 10031), Pseudomonas aeruginosa (ATCC 27853) and gram positive Staphylococcus aureus (ATCC 25923).

The present invention relates also to a method of killing or inhibiting growth of microbes, comprising the step of treating said microbes with a peptide(s) or their variants described here. In one embodiment the peptide or a variant there of exhibits an activity against microorganisms, in particular against gram positive and/or gram negative bacteria, in particular against the families Staphylococcaceae and Enterobacteriaceae, in particular against microorganisms of the species S. aureus and/or E. coli. In one embodiment the peptide or a variant thereof exhibits an activity against fungi. In still further embodiment the peptide or a variant thereof exhibits activity against both fungi and bacteria. The activities and other properties of the peptides have been discussed above in connection of other embodiments.

Catheter acts as a carrier of bacteria through attachment to the surface and then to the lumen of urethra. Most of the catheters are made of silicone rubber where microbes adhere easily to form biofilms and cause infections. Several strategies have been developed to overcome these problems by using antibiotic compounds such as rifampin and minocycline, or silver coating on catheter surfaces. However, the use of antibiotics risk development of bacterial resistance and antibiotic efficacy in the clinical applications is not well known. Silver-coated catheters were found ineffective in in-vitro studies.

Catheter-associated urinary tract infections (CAUTI) can be prevented by using antimicrobial peptide (AMP)-coated urinary catheters, which also prevent the spread of antibiotic resistance.

It should also be understood that the peptide(s) or their variants of the present invention can be used with various uses requiring antimicrobial activity.

It is to be understood that the terminology employed herein is for the purpose of description and should not be regarded as limiting.

The features of the invention described here as separate embodiments may also be provided in combination in a single embodiment. Also various features of the invention described here in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. It should be understood, that the embodiments given in the description above are for illustrative purposes only, and that various changes and modifications are possible within the scope of the disclosure.

A listing of the cited references will be given below. The contents of all citations are herewith incorporated by reference.

The following non-limiting examples illustrate the invention.

EXAMPLES Example 1: Total Plant DNA Isolation

Fresh and young leaves of Empetrum nigrum L. were surface sterilized with 70% ethanol (v/v) for 1 min and in sodium hypochlorite (3.5% v/v) for 5 min and used for the isolation of genomic DNA (Pirttilä et al. 2001).

Example 2: Metagenomic Library Construction and Screening for Antibacterial Activity

Plant DNA isolated from E. nigrum was dissolved in sterile water to a concentration of 0.1 μg μl⁻¹. The DNA was then subjected to preparative pulsed-field gel electrophoresis in a CHEF-DRII (Bio-Rad) system. The electrophoresis conditions (pulse intervals and durations) were: N/S—60 s and E/W—60 s for 6 h; N/S—90 s and E/W—90 s for 6 h; N/S—99 s and E/W—99 s for 6 h, respectively, with a voltage of 6 V/cm, a 120° fixed angle and using a 0.15× Tris-borate-EDTA (TBE) buffer. During the electrophoresis, the temperature was maintained at 10° C. After electrophoresis, a strip from each side of the gel was cut off and stained with ethidium bromide to visualize the DNA. The high-molecular-weight DNA was then excised from the remaining unstained part of the gel and electro-eluted for 1 h at 100 V in a dialysis bag containing 0.5×TBE. Amplification by primers specific for fungi and bacteria was done as previously (Koskimäki et al. 2010, Tejesvi et al. 2010) to confirm the separation of microbial DNA. For cloning, the DNA of about 25-30 kb was end repaired to produce 5′-phosphorylated DNA and ligated to blunt-ended dephosphorylated pCC1FOS™ vector. The ligation mixture was packaged into lambda phages using MaxPlax Lambda Packaging Extracts (Epicentre). The packaged library was then transduced into E. coli EPI-300, and the transformants were selected on LB agar plates supplemented with chloramphenicol. The packaged fosmid library was stored in cryotubes as clone pools containing approximately 10³ clones per pool until screening.

The fosmid library screening was performed as follows: clone pools were thawed and spread onto 150-mm LB agar plates supplemented with chloramphenicol to obtain ˜1000 colonies per plate. The library plates were incubated overnight at 30° C. followed by incubation at room temperature (RT) for additional 3-5 days. The plates were overlaid with top agar containing exponentially growing Staphylococcus aureus and incubated overnight at 37° C., followed by further incubation at RT for 3-5 days. Colonies with antibacterial activity were identified by a zone of inhibition of S. aureus growth. Such colonies were picked through the top agar and separated from the chloramphenicol-sensitive assay strain (S. aureus) by streaking onto LB plates containing ampicillin and chloramphenicol. Restriction analysis of the selected antibacterial fosmid clone was carried out by digestion with BamHI and electrophoresis.

Example 3: Strains, Plasmids and Growth Conditions

EPI-300™-T1® Phage T1-resistant E. coli cultures were grown at 37° C. on Luria-Bertani (LB) agar or in LB broth+10 mM MgSO₄ supplemented with the appropriate antibiotics. The following antibiotic concentrations were used for the E. coli strain: chloramphenicol 12.5 μg ml⁻¹ and ampicillin 100 μg ml⁻¹. Plasmid pCC1FOS™ (Epicentre, Madison, USA) that carries two origins of replication, a single copy origin (ori2) and an inducible high copy origin (oriV) was used to construct the metagenomic library from endophytes of Empetrum nigrum and for subcloning the genes conferring such antibacterial activity. The pET11-c vector was used to express the genes responsible for the antibacterial activity in the host strain E. coli BL21 (DE3) gold.

Example 4: Subcloning and Sequencing of Clone pFosS1A

The antibacterial fosmid clone selected from the agar overlay assay was named pFosS1. The metagenomic fosmid was isolated using the Plasmid Midiprep Kit (Qiagen) and subjected to partial digestion with Sau3AI (0.1 U μl⁻¹ of DNA, 37° C. for 15 min) and electrophoresis for size selection of the DNA and subcloning. Fragments greater than 1.5 kb were extracted from the gel, end-repaired and ligated into blunt-ended dephosphorylated pCC1FOS™. The ligation mixture was transformed into E. coli and the recombinant clones were screened by the agar overlay assay and spread onto LB plates supplemented with chloramphenicol. The subclones showing clear zones of inhibition of S. aureus were analysed by gel electrophoresis after digestion with BamHI to select the subclone harboring the smallest insert of ˜1.8 kb. This subclone was named pFosS1A and sequenced with the primers pCC1 forward and pCC1 reverse according to the manufacturer's instructions (Abi 3730 DNA Analyser, Abi Prism BigDye Terminator Cycle Sequencing Kit, Applied Biosystems, Warrington, UK). The open reading frame contained within the subclone pFosS1A was named En-MAP1 and analyzed by the BLAST program of Genbank as well as SignalP and pfam.

Example 5. Construction and Screening of the Metagenomic Library

The band corresponding to endophytic DNA was separated from the Empetrum nigrum genomic DNA, which remained in the wells of the agarose gel after PFGE electrophoresis. Presence of endophytic DNA in the band was confirmed by amplification of PCR products with primers specific for fungi and bacteria. Approximately 8,000 metagenomic clones were obtained from 20 μg DNA. Screening of the metagenomic library by the agar overlay method resulted in the identification of one antibacterial clone exhibiting an inhibition zone for S. aureus. However, growth inhibition of the host E. coli was not observed. Restriction fragment analysis revealed that the clone carried an insert DNA of over 30 kb in size. A secondary library was generated from the antibacterial clone to select antibacterial subclones and to characterize the individual gene(s) responsible for the antibacterial activity. Restriction fragment analysis of antibacterial subclones identified the smallest insert of 1.8 kb in subclone pFosS1A, which still exhibited growth inhibition of S. aureus in the agar overlay assay (FIG. 1).

Example 6: Fractionation and Analysis of Clone Supernatant

E. coli cells carrying the subclone pFosS1A and control (empty vector) were grown overnight at 37° C. in LB-broth containing chloramphenicol. These cultures were used as inocula for the copy number amplification procedure. One volume of these cultures was added to 10 volumes of fresh LB+chloramphenicol and 1/100 of CopyControl Induction Solution (Epicentre) was added to the media to induce clones to high copy number. After vigorous shaking of cultures at 37° C. for 20 h, the supernatant was separated from bacterial cells by centrifugation for 20 min at 3040×g at 4° C. The supernatant was freeze-dried by Heto PowerDry LL1500 freeze dryer (ThermoElectron, Mukarov, Czech Republic). The freeze-dried broth was weighed and 50 mg was dissolved to 2 ml of distilled water. The material was kept in ultrasonicator for 20 minutes, centrifuged for 10 minutes, filtered (GHP Bulk Acrodisc 13, Pall Life Sciences) and fractioned by semi preparative High Pressure Liquid Chromatography (HPLC). The fractions were then tested for antibacterial activity by the 96-well plate standard method using S. aureus as the test strain. Supernatants of subclone pFosS1A and control were analyzed for small molecules by Alliance 2690 HPLC (Waters, Milford, Mass., USA) combined with Micromass LCT Time-of-flight mass spectrometry (TOFMS) (Micromass, Altrincham, UK).

Example 7. Sequence Analysis of the Antibacterial Subclone

The insert of subclone pFosS1A was completely sequenced in both directions and it contained a unique open reading frame of ˜1650 bp. The putative ribosome-binding site and promoter sequence are present at ˜35/−10 upstream region from the initiation codon. The nucleotide sequence was subjected to BLAST analyses against sequences present in the Genbank databases but no similarity to any known sequence was identified. This suggested that the isolated gene encoded for a protein of novel structure and therefore the protein was named Empetrum nigrum metagenomic antibacterial protein 1 (En-MAP1). Analysis of the deduced amino acid sequence revealed that En-MAP1 encodes for a protein of 549 amino acids (FIG. 2), sharing the highest similarity of 32% to a hypothetical protein from Pseudozyma hubeiensis and no similarity to any protein of known function. SignalP analysis indicated that the amino acid sequence of En-MAP1 had no putative amino-terminal signal sequences for secretion or translocation. When the deduced amino acid sequence was analyzed for conserved motifs using the pfam protein family database, three pentatricopeptide repeat-motifs were identified at positions 77 to 107, 126 to 153 and 392 to 420 aa (FIG. 2). En-MAP1 was predicted to be a soluble protein having no transmembrane region analyzed by TMpred and PSORT. The residues 147-176 also consisted a predicted coil-coil region, which is typical for proteins involved in protein-protein interactions, and a possible leucine zipper starting at residue 490, analyzed by PSORT.

Example 8: Protein Expression in pET23(b)

The gene En-MAP1 was amplified using primers with Nde1 and Sal1 restriction sites pFosS1F (CATATGAGACTAGTAGCTCATCCTGTTCCTGATGC; SEQ ID NO: 2) and pFosS1R (GTCGACTTATTAACGAGATGACGTCCTCTGCTGTACG; SEQ ID NO: 3). The amplification products were cloned into pET23(b) vectors, transformed into XL1 competent cells, and the gene identity was confirmed by sequencing. The expression studies were done using E. coli strains BL21 pLysS and BL21 pRARE as the hosts. The protein was expressed in both strains as inclusion bodies, which were isolated (van Lith et al. 2007). The inclusion bodies were suspended in 5M guanidine hydrochloride/0.2 M sodium phosphate buffer (pH 7.0) and the protein was refolded on HisTrap Column (GE Healthcare Life Sciences) using a linear buffer exchange from 3 M guanidine/0.2 M sodium phosphate (pH 7.0) to 0.2 M sodium phosphate (pH 7.0) over 4 h in AKTA FPLC, and finally eluted with 50 mM EDTA/20 mM sodium phosphate buffer (pH 7.0). The nucleotide sequence of En-MAP1 has been deposited to the GenBank under accession number KC466596.

Example 9: Antibacterial Activity Analysis of Protein

Both folded and unfolded proteins were tested for antibacterial activity against S. aureus by pipetting 10 μg of protein on the S. aureus culture on an LB plate. The activity was also tested in folded and unfolded protein digested with trypsin in 0.01% acetic acid at concentrations of 30 and 60 μg/ml.

Example 10: Prediction of Antimicrobial Peptides and Peptide Synthesis

The protein En-MAP1 was in silico-trypsin digested (http://au.expasy.org) and 12 peptides (Met1-Met12) were predicted (http://www.bicnirrh.res.in/antimicrobial) to be antimicrobial by three different algorithms (Support Vector Machine (SVM) classifier, Random Forest Classifier and Discriminant Analysis Classifier) and by APD2 (http://aps.unmc.edu/AP/prediction/prediction_main.php). Synthesized peptides were purchased from GenScript, USA.

Example 11: Antimicrobial Activity of Synthesized Peptides

The radial diffusion assay (RDA) was carried out as described by Andersen et al. (2010). Briefly, 30 ml of 1/10 Muller-Hinton broth (MHB) supplemented with 1% agarose and 5.0×10⁵ CFU/ml S. aureus or E. coli or K. pneumoniae, P. aeruginosa cells was poured into a single-well omnitray (Nunc) and overlaid with a TSP 96-well plate. One hundred μg of each synthesized peptide was tested. The peptides were also tested against Fusarium oxysporum and Verticillium dahliae, for which ⅓ potato dextrose agarose was used. To test the synergistic effect of peptides, each peptide was mixed in equimolar concentrations. Mix1 (met1-12), Mix2 (met3, 4 and 5), Mix3 (met 8, 9 and 10), Mix 4 (met11, 12) and Mix5 (8, 9, 10, 11, 12) were prepared and tested against E. coli and S. aureus. Gentamicin and vancomycin were included as positive controls for bacteria and amphotericin B was used as the control for fungi.

Minimum inhibition concentrations (MICs) were determined against Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 25923), Klebsiella pneumoniae (ATCC 10031) and Pseudomonas aeruginosa (ATCC 27853). Also clinical strains of E. coli, K. pneumoniae, E. cloacae, P. aeruginosa, Serratia marcescens, Proteus mirabilis, S. pneumoniae, Acinetobacter baumannii, A. johnsonii and S. aureus were used for MICs assays. Additionally, clinical strains of yeast including Candida albicans, C. glabrata, C. parapsilosis and C. quillermondiae were used. The susceptibility of these microorganisms to Chain peptides were determined using micro broth dilution assay. Colonies of the respective microorganism from Muller Hinton (MH) agar plates incubated overnight were suspended in MH broth media and final concentration of microorganism was adjusted to 5.0×10⁵ cfu/ml. An aliquot of 10 μl of each Chain peptide, or gentamicin, tetracycline as reference antibiotics were added in differing concentrations along with 90 μl of bacterial suspension to 96 well polypropylene plates and incubated at 37° C. for 20 to 24 hours. Concentrations of Chain peptides and reference antibiotics ranged from 0.125 to 128 μg/ml and the MICs were recorded as the lowest concentration with no visual growth of bacteria. Similarly, antifungal MICs were tested in Potato dextrose broth.

Example 12: Expression Analysis of the Antibacterial Clone

The subclone expressing pFosS1A was analyzed by HPLC-MS for possible production of small antimicrobial molecules in the liquid medium and compared with the control (empty vector). The chromatograms and spectra of the peaks for the antibacterial clone and the control were identical. The medium was fractioned and tested for antibacterial activity against S. aureus, but no activity was detected. This suggested that the antibacterial activity against S. aureus was not from a metabolite generated by En-MAP1 activity.

The gene En-MAP1 was then cloned into the expression plasmid pET23(b) to analyze whether the antibacterial activity was due to the protein itself. The resulting construct pET23(b)-FosS1A contained the En-MAP1 gene in-frame. When transformed into E. coli expression strain BL21 (DE3) pLyseS and BL21 (DE3) pRARE, a protein of approximately 63 kDa (predicted mass 63.3 kDa) was produced in the cell extracts of induced, but not in the uninduced cultures. The resulting protein includes the amino acid sequence MHHHHHHM- prior to the first amino acid of the protein sequence. The protein was expressed in both strains as inclusion bodies and they were purified and folded in a His-Trap column, resulting in about ˜1 mg of pure folded protein. The folded protein was tested for antibacterial activity against S. aureus and no activity was observed. To test whether a shorter fragment was responsible for the antibacterial activity due to alternative translation starting sites, three constructs encoding shorter fragments of En-MAP1 were designed and expressed, but no activity was observed. However, when the folded full En-MAP1 protein (SEQ ID NO: 1) was digested with trypsin, antibacterial activity was observed for up to two hours after digestion (data not shown). No activity was detected in the trypsin digest of the unfolded protein. This suggested that the antimicrobial activity resulted from fragmentation of the protein, producing a peptide, which contained an internal trypsin cleavage site that was protected by the folded structure.

To further identify the peptide responsible for antimicrobial activity, the En-MAP1 protein was digested in silico and the peptides, which were predicted to be antimicrobial, were synthesized. Cleavage sites for several restriction enzymes, proteases and chemical compounds, such as ArgC proteinase, Asp-N endopeptidase (EC 3.4.24.33), chymotrypsin-HS30 (EC 3.4.21.1), clostripain, CNBr (EC 208-051-2), formic acid, Lys-C, iodosobenzoic acid, proline endopeptidase, and trypsin were included in the in-silico analysis. Antimicrobial activities of the peptide fragments were predicted using four different algorithms (Support Vector Machine (SVM) classifier, Random Forest Classifier, Discriminant Analysis Classifier and APD2).

The majority of these peptides were from tryptic digest predictions, while three peptides (shown as Met10, Met11 and Met12 in FIG. 3 and Chain 100 defined by SEQ ID NO: 4, Chain 200 defined by SEQ ID NO: 5 and Chain 300 defined by SEQ ID NO: 6, respectively in tables (1, 2a, 2b, 2c, 3a, 3b and 3c) and sequence listing) resulted from Asp-N-endopeptidase16, chymotrypsin-HS30 and CnBr digestions, respectively. Eight of these peptides contained an internal trypsin cleavage site.

Example 13: Salt, pH and Thermal Stability

Thermal stability was evaluated by diluting peptides to the concentration of 2 mg/ml in PBS buffer (pH 7.4) and incubating at different temperatures, such as +4° C., 25° C. (RT), 37° C. and 45° C., peptides stored at −20° C. were used as control. After each time interval, 100 μl (2 mg/ml) of peptides were taken and stored at −20° C. for radial diffusion assay to determine the antibacterial activity (FIG. 8). Peptides were also tested by diluting them at different pH values starting from pH 4 to 9. The effect of NaCl on the antimicrobial activity was tested by adding different concentrations (50, 100 and 200 mM) of NaCl to MH medium and the minimum inhibitory concentrations were tested against 4 ATCC bacterial strains.

Example 15: Bacterial Adherence on Coated and Uncoated Silicon Catheters

The coated (Chain 105 or Chain 201) and uncoated silicon catheters were cut into 0.5 cm pieces and placed in 24 well plates suspended with 1 ml of 5×10⁵ CFU/mL bacterial (E. coli and S. aureus) culture in phosphate buffer saline (PBS). Samples were incubated at 37° C. for 6 h at 150 RPM. After incubation, each catheter piece was rinsed with 1 ml of PBS for 2 times using fresh PBS. The catheter pieces were transferred to Eppendorf tubes and 500 μl of PBS was added, sonicated in water bath for 2 minutes, vortexed for 5 sec, serially diluted, and CFUs were determined.

Example 14: Preparation of Cells for Transmission Electron Microscopy (TEM)

E. coli and S. aureus were grown to mid-exponential phase and diluted in Muller Hinton broth (MHB) medium to a cell density of 0.1 by taking absorbance at 600 nm and incubated at 37° C. for 1 h with 10 μg/ml Chain peptides. After incubation, an equal volume of 2% glutaraldehyde in 0.1 M phosphate buffer was added and the cells were pelleted by centrifugation at 5000 rpm for 2 minutes, and the cell pellet was fixed with 1% glutaraldehyde in 0.1 M phosphate. Cells were post-fixed with osmium tetroxide, dehydrated using increasing concentrations of acetone or alcohol, and embedded in plastic resin (Epon). Ultrathin sections (70-80 nm) were post-stained with uranyl acetate and lead citrate before observation with TEM. Microscopy was performed with a Tecnal G2 Spirit 120 kV TEM with Veleta and Quemesa CCD cameras.

TABLE 1 The peptide variants generated using tryptophan, lysine and arginine residues at various places and predicted by statistical models using CAMP database (SVM, RF, ANN and DA). Ali- Sl. SVM RF DA phatic Instability Net CAMP No Name Sequence values^(a) values^(b) ANN^(c) values^(d) Index^(e) Index^(f) charge Identities database^(g) 4 Chain100 DCWSAMIRLHAKYNQV 0.156 0.4615 AMP 0.012 79 14.7 1 6/11 (54%) CAMPSQ4068 7 Chain101 KIRLHRKRLRK 0.976 0.725 AMP 0.995 106 48 7 6/11 (54%) CAMPSQ73 8 Chain102 KKRLHRKRLRK 0.997 0.6695 AMP 0.995 70 85 8 8/11 (72%) gi_33736048 9 Chain103 KLRLHAKRLRK 0.893 0.696 AMP 0.922 115 66 6 No hits nil 10 Chain104 RKWRAMIRLHAKRLRK 0.989 0.7955 AMP 0.871 85 41 8 6/11 (54%) gi_74472293 11 Chain105 RKWRAMIRLHAKWLRK 0.997 0.8375 AMP 0.852 85 29 7 6/11 (54%) gi_67584689 12 Chain106 WIRLHWKRLRK 1 0.927 AMP 0.995 106 53 5 5/11 (45% gi_59754113 13 Chain107 WWRLHAKKKLW 1 0.97 AMP 0.993 80 22.9 4 4/11 (36%) CAMPSQ4044 14 Chain108 WWRLHAKRKLW 1 0.936 AMP 0.994 80 52 4 6/11 (54%) CAMPSQ4044 15 Chain109 WWRLHAKWKLW 1 0.9765 AMP 0.996 80 22 3 4/11 (36%) gi_59754171 16 Chain110 KLKRAMIRLHAKKRLK 0.916 0.8285 AMP 0.926 110 34 8 7/16 (44% gi_75999248 17 Chain111 KLKRAMIRLHAKKWRW 0.996 0.869 AMP 0.816 85 54 7 No hits nil 18 Chain112 RLKRAMIRLHAKKWRW 0.995 0.861 AMP 0.826 85 60 7 No hits nil 19 Chain113 RWWRAMIRLHAKKWRW 1 0.8495 AMP 0.97 61 80 6 7/16 (44% gi_59754035 20 Chain114 WWRLHAAKKIL 1 0.9625 AMP 0.991 124 19 3 5/11 (45% CAMPSQ4137 21 Chain115 WWRLHAKKKCW 0.998 0.9205 AMP 0.97 45 30 4 4/11 (36%) CAMPSQ4044 22 Chain116 WWRLHAKKKFW 1 0.954 AMP 0.995 45 9.09 4 4/11 (36%) CAMPSQ4044 23 Chain117 WWRLHAKKKIW 1 0.969 AMP 0.993 80 1.37 4 3/11 (27%) CAMPSQ4009 24 Chain118 WWRLHAKKKRW 1 0.9075 AMP 0.996 45 90 5 5/11 (45% gi_3407608 25 Chain119 WWRLHAKKKWR 1 0.907 AMP 0.993 45 9 5 4/11 (35%) gi_59754211 26 Chain120 WWRLHAKKKWW 1 0.968 AMP 0.998 45 9.09 4 5/11 (45% CAMPSQ4044 25 Chain121 WWRLHAKLKLW 1 0.9585 AMP 0.995 115 7.4 3 4/11 (36%) CAMPSQ4044 28 Chain122 WWRLHAKRKRW 1 0.8155 AMP 0.997 44 120 5 5/11 (45% gi_3407608 29 Chain123 WWRLHAKWRWR 1 0.928 AMP 0.998 44 61 4 6/11 (54%) gi_59754169 30 Chain124 WWRLHARKRWW 1 0.933 AMP 0.999 44 90 4 5/11 (45% gi_3407608 31 Chain125 WWRLHAWKWRR 1 0.936 AMP 0.998 44 61 4 7/11 (63%) gi_59754006 5 Chain200 NRIVQQRTSSR 0.028 0.3175 NAMP 0.006 61 53 3 No hits found nil 32 Chain201 KWIVWRWRFKR 1 0.977 AMP 0.96 61 69 5 6/11 (54%) gi_59754085 33 Chain202 RKIVKKRTFKR 0.988 0.6975 AMP 0.997 61 47 7 6/11 (54%) gi_33735965 34 Chain203 RRIVKLRWFKR 1 0.8035 AMP 0.944 97 128 6 No hits nil 35 Chain204 RRLIWRRFKWLR 1 0.889 AMP 0.978 97 118 6 5/11 (45% gi_59754033 36 Chain205 KRIVRWRTRKR 0.995 0.72 AMP 0.956 61 112 7 4/11 (36%) gi_3407606 37 Chain206 KRIVRWRWRKR 1 0.787 AMP 0.912 61 164 7 5/11 (45% gi_59754033 38 Chain207 KRIVRWRKLKRK 0.999 0.8415 AMP 0.943 89 90 8 6/11 (54%) CAMPSQ3545 39 Chain208 WRILRWRKLKR 1 0.9165 AMP 0.984 106 110 6 5/11 (45% CAMPSQ3545 40 Chain209 WRIVRWRKLKR 1 0.9055 AMP 0.971 97 67 6 6/11 (54%) CAMPSQ3545 41 Chain210 WRIVQWRKLKR 0.999 0.896 AMP 0.844 97 15 5 4/11 (36%) gi_59754101 42 Chain211 KRIVRRRTFKR 1 0.6455 AMP 0.999 61 162.35 7 6/11 (54%) gi_75999237 43 Chain212 KRWRKWRLFKR 1 0.803 AMP 0.95 35 106 7 5/11 (45% gi_74472319 44 Chain213 NRIVLLRTFKR 0.752 0.6575 AMP 0.983 132 28 4 No hits nil 45 Chain214 NRIVKKRTFKR 0.937 0.6525 AMP 0.983 132 28 4 6/11 (54%) CAMPSQ3535 46 Chain215 RKIVKRRTFKR 0.997 0.672 AMP 0.998 61 99 7 No hits nil 47 Chain216 RKIVWWRTFKR 0.997 0.8025 AMP 0.963 61 20 5 4/11 (35%) gi_62788246 48 Chain217 RLIVRRRTFKR 0.999 0.678 AMP 0.998 97 132 6 No hits nil 49 Chain218 RRIVRKKTFKR 0.997 0.652 AMP 0.968 61 80 7 6/11 (54%) gi_75999276 50 Chain219 RRIVWRRTFKR 1 0.6675 AMP 0.977 61 132 6 4/11 (36%) CAMPSQ3545 51 Chain220 RWIVQRRTFKR 1 0.679 AMP 0.986 61 184 6 No hits nil 52 Chain221 RVIVRRRTFKR 0.999 0.6545 AMP 0.996 88 132 6 No hits nil 53 Chain222 WKIVKKRTRRR 0.991 0.788 AMP 0.985 61 124 7 4/11 (36%) gi_74472305 54 Chain223 WRIVRRRTFKR 0.999 0.6965 AMP 0.989 62 132 6 4/11 (36%) gi_3407608 6 Chain300 YDKGFGLFKKM 0.705 0.2515 AMP 0.11 35 31 2 No hits nil 55 Chain301 IIKRFRLFKKL 0.989 0.9255 AMP 0.999 141 10 5 5/11 (45% gi_115794206 56 Chain302 ILKRWWLFKKL 1 0.9715 AMP 0.996 141 91 4 5/11 (45% gi_59754119 57 Chain303 IWKRFRLFKKR 1 0.883 AMP 0.976 71 55 6 5/11 (45% gi_115794207 58 Chain304 IWKRFRLFKKW 1 0.955 AMP 0.98 71 25 5 5/11 (45% CAMPSQ754 59 Chain305 RLKWFWLRKLK 0.999 0.95 AMP 0.947 106 14.7 5 4/11 (36%) gi_59754121 60 Chain306 RLKRWRLFRKR 1 0.6875 AMP 0.917 70 134 7 6/11 (54%) gi_62788246 61 Chain307 RLKWFWLFRKR 0.999 0.8795 AMP 0.946 106 60.7 6 5/11 (45% gi_59754067 62 Chain308 RLKWFLLFRKR 0.992 0.8335 AMP 0.94 106 31 5 5/11 (45% gi_27291218 63 Chain309 WRKWFWLFKKR 1 0.9455 AMP 0.995 35.4 36.2 5 6/11 (54%) CAMPSQ354 64 Chain310 KRKWRWLFKKL 0.999 0.8745 AMP 0.944 70 28 5 6/11 (54%) CAMPSQ461 65 Chain311 KLKWFWLFKKR 0.999 0.954 AMP 0.91 70 21 5 4/11 (36% gi_10064836 66 Chain312 KLKKFKLFKKR 0.999 0.819 AMP 0.96 70 −11.5 7 8/11 (72%) gi_115794212 67 Chain313 RLKRFRLFRKRK 0.999 0.722 AMP 0.994 65 56 8 5/12 (42% gi_115794207 68 Chain314 KRKRFRLFKKR 1 0.6525 AMP 0.998 35 84 8 6/11 (54%) gi_115794207 69 Chain315 RLKRFRLFKKL 0.997 0.7565 AMP 0.982 106 9.6 6 5/11 (45% gi_115794207 70 Chain316 RRKRFRLFKKM 0.985 0.5865 AMP 0.998 35 106 7 7/11 (63%) CAMPSQ114 71 Chain317 RRKRFRLFRRK 1 0.639 AMP 0.998 36 142 8 7/11 (63%) gi_112062720 72 Chain318 RWKRFRLFKKR 1 0.7545 AMP 0.952 35 106 7 5/11 (45% gi_115794208 73 Chain319 RWKRFRLFKKW 1 0.8795 AMP 0.954 35 77 6 5/11 (45%) gi_115794208 74 Chain320 WKKGFGLFKKM 0.998 0.713 AMP 0.967 35 17 4 6/11 (54%) CAMPSQ3086 75 Chain321 WKKRFRLFKKL 1 0.878 AMP 0.905 70 17 6 6/11 (54%) CAMPSQ3086 76 Chain322 WLRRFRLFRRL 1 0.769 AMP 0.986 106 141 5 6/11 (54%) gi_62788246 77 Chain323 RLKRFLLFRKRL 0.996 0.687 AMP 0.988 130 56 6 7/12 (58%) CAMPSQ2349 78 Chain324 KRKWFWLFKKL 0.999 0.8745 AMP 0.944 70 28 5 6/11 (54%) CAMPSQ461 76 Chain325 KLKRFRLFKKR 0.998 0.712 AMP 0.977 70 39 7 6/11 (54%) gi_115794210 ^(a)SVM: support vector machines; ^(b)RF: random forest; ^(c)ANN: artificial neural networks; ^(d)DA: discriminant analysis; ^(e)Aliphatic index: positively correlated with thermostability; ^(f)Instability Index: <40 is considered stable; ^(g)CAMP database - http://www.camp.bicnirrh.res.in

The antimicrobial activity of the twelve peptides (Met1-Met12) was tested against S. aureus, E. coli, and Verticillium dahliae. Initial screening was performed by the radial diffusion assay to confirm the antimicrobial activity. Peptides Met1, Met3, Met4, Met5, Met10, Met11 and Met12 were active against E. coli (FIG. 3) and Met3, Met10 and Met11 exhibited activity against S. aureus, each at the concentration of 100 μg/well. Synergistic effect of the peptides was also tested by mixing equimolar concentrations of peptides, but no significant difference in activity was seen. Moderate antifungal activity was observed for Met8 against Verticillium dahliae (data not shown). Minimal inhibitory concentration (MIC) assays were carried out for all samples against E. coli and S. aureus. Met11 was active at the concentration of 95 μM and the rest of the peptides had a MIC of >190 μM. All peptides were predicted to have an alpha helical structure except Met12.

By using rational design techniques, we have designed variants of peptides by incorporating or replacing various amino acids in the original peptides. Thus, we have designed and modified Chain 100, Chain 200 and Chain 300 with tryptophan (W), arginine (R) and lysine (K) at various positions to improve antimicrobial activity (FIGS. 4a-c and 5a-c ). In some peptides we have also used other amino acids such as Leucine (L), Cysteine (C), Isoleucine (I), Phenylalanine (F) and Alanine (A). For synthesis, 32 variants and 3 original peptides were selected based on the various parameters such as positive charge, aliphatic index and instability index. Peptides variants were tested by using radial diffusion assay against Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 25923), Klebsiella pneumoniae (ATCC 10031) and Pseudomonas aeruginosa (ATCC 27853) (FIGS. 6a-c ). The zone of inhibition ranged between 10-18 mm for Escherichia coli and Staphylococcus aureus, 6-18 mm & 8-18 mm for Pseudomonas aeruginosa and Klebsiella pneumonia respectively (Table 2). For Gentamicin it was between 22-24 mm. Antifungal activity was tested for promising antibacterial peptides (Chains 104, 105, 109, 201, 204, 306, 307, 308, 310) against Aspergillus flavus (DSM 1959) and Penicillium chrysogenum (DSM 1075). All these peptides has activity at a concentration of 20 μg, Amphotericin B was used as a positive control at 20 μg (FIG. 7).

Minimum inhibition concentrations (MICs) were tested by microbroth dilution method and Chain 104, 105 and 109 inhibited the growth of Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 25923), Klebsiella pneumoniae (ATCC 10031) and Pseudomonas aeruginosa (ATCC 27853) between 1-8 μg/ml respectively (Tables 3a, 3b and 3c). The membranolytic activities of the peptides were tested by measuring the release of hemoglobin from erythrocytes of fresh blood donated by volunteers. Hemoglobin levels were determined spectrometrically by taking OD at 540 nm by following the protocol of Schmidtchen et al., 2011. The percent hemolysis ranged between 0.1 to 9% indicating that most of these peptides do not have any effect on the host at a concentration of 128 μg/ml (Table 3).

Twelve peptides, Chain 104, Chain 105, Chain 109, Chain 201, Chain 204, Chain 304, Chain 306, Chain 307, Chain 308, Chain 309, Chain 310 and Chain 311 were found to be very active against the four ATCC strains and therefore, were synthesized as D-form amino acids and tested against clinical strains of E. coli, K. pneumoniae, E. cloacae, P. aeruginosa, Serratia marcescens, Proteus mirabilis, S. pneumoniae, Acinetobacter baumannii, A. johnsonii and S. aureus. Clinical strains of yeasts including Candida albicans, C. glabrata, C. parapsilosis and C. quillermondiae were also tested with the 12 Chain peptides. The minimum inhibitory concentration (MICs) varied between these peptides and are presented in Tables 4a, 4b, 4c and 5a, 5b, 5c. Peptides Chain 105, 201 and 308 are broad spectrum antimicrobials with MICs between 0.5-32 μg/ml against all the bacteria and yeasts tested, except Serratia marcescens and Proteus mirabilis, against which the MICs were between 64-128 μg/ml. Peptide Chain 306 has narrow spectrum activity against E. coli at 1 μg/ml and for the rest of the bacterial strains at >32 μg/ml (FIG. 10c ).

Peptides Chain 104, Chain 105, Chain 201, Chain 308, Chain 310 were tested against antibiotic-sensitive strains of S. aureus RN4220 and methicillin resistant strains of S. aureus COL (MRSA). Chain peptides comprising of either L- or D-form amino acids were tested against these bacteria, and the D-form peptides were found have better activity compared to L-form (Table 6). Synergistic activity of chain peptides along with Ertapenem (4 μg/ml) was tested to know whether it will influence the activity against MRSA strains. All the Chain peptides were found to have antibacterial activity against MRSA strains with MICs at the range of 0.03 to 4 μg/ml. Chain 310 has the best antibacterial activity against the MRSA strains with a MIC of 0.06 & 0.03 μg/ml along with Ertapenem (4 μg/ml) for both forms of L and D-peptides (Table 6).

Many antimicrobial peptides (AMPs) have broad spectrum antimicrobial activity against clinical strains of bacteria and fungi. Antimicrobial peptides form secondary structures by electrostatic interactions with bacterial membranes by a salt-sensitive step. Therefore high salt concentrations in the human body fluids can deactivate many AMPs and it is essential to develop salt-tolerant AMPs for applications in healthcare. However, it is well known that physiological condition, pH, temperature and high salt concentrations will influence the activity of these peptides. We have evaluated pH, salt- and thermostability of Chain 104, 105, 201, 204, 306 and 308 and have found that these peptides are not hindered by pH or temperature even upto 45° C. for over 14 days (FIGS. 8 & 9). However, there is a 2-fold increase in MIC values of Chain 104, 105, 201, 204, 306 and 308 upon using 200 mM NaCl concentration.

Electron microscopy studies were needed to know the AMP mechanism of action on the cells upon treatment with 5× MICs on the cell surface, as well as the intracellular alterations. AMPs typically cause multiple stresses on the cell membranes even at low concentrations. E. coli has a complex cell structure with cytoplasmic membrane (7 nm), peptidoglycan layer (7-8 nm) and an outer membrane (10-15 nm). Antibiotic resistance of E. coli is due to the presence of inner peptidoglycan along with the outer membrane. Upon incubation with Chain peptides (105, 201, 308), almost all E. coli cells had lost their rod-shaped structural integrity, and accumulation of granular structures, bubble-like structure protruded from cell surface and distortions were seen in cells (FIG. 11). The interaction of the Chain peptides with S. aureus lipid bilayer can be seen with an expansion of membrane area. We also observed spreading of cytoplasmic membrane and spherical mesosomes as intracellular bilayer membranes and mesosome-like structures formed within the cells.

Catheter-associated infections were initiated by the planktonic bacterial cells adherence to the biomaterial surface by colonization and biofilm formation. Catheters immobilized with Chain 201 or Chain 105 posed excellent antimicrobial activity against E. coli and S. aureus. A reduction of more than 70% and 30% of living cells of S. aureus and E. coli was observed, respectively (FIG. 12).

TABLE 2a Antibacterial activity of peptide variants by radial diffusion method. Inhibition zone is provided in millimeters for respective bacterial pathogens. Inhibition zone (mm)* Pseu- Escherichia Staphylococcus domonas Klebsiella Peptides coli aureus aeruginosa pneumoniae Chain200 — — — — Chain201 16 15 15 14 Chain202 — — — — Chain203 16  8  5 10 Chain204 18 15 18 15 Chain205  6  5 — — Chain206 14 10 — — Chain207 — — — — Chain208 15 12 10 12 Chain209 14 11 —  8 Chain210 13 10 —  6 Gentamycin 22 24 24 22 Test concentration: Gentamycin - 5 μg; Peptides - 50 μg Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 25923), Klebsiella pneumoniae (ATCC 10031) and Pseudomonas aeruginosa (ATCC 27853) *Values in diameter including the wells.

TABLE 2b Antibacterial activity of peptide variants by radial diffusion method. Inhibition zone is provided in millimeters for respective bacterial pathogens. Inhibition zone (mm)* Pseu- Escherichia Staphylococcus domonas Klebsiella Peptides coli aureus aeruginosa pneumoniae Chain200 — — — — Chain201 16 15 15 14 Chain202 — — — — Chain203 16  8  5 10 Chain204 18 15 18 15 Chain205  6  5 — — Chain206 14 10 — — Chain207 — — — — Chain208 15 12 10 12 Chain209 14 11 —  8 Chain210 13 10 —  6 Gentamycin 22 24 24 22 Test concentration: Gentamycin - 5 μg; Peptides - 50 μg Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 25923), Klebsiella pneumoniae (ATCC 10031) and Pseudomonas aeruginosa (ATCC 27853) *Values in diameter including the wells.

TABLE 2c Antibacterial activity of peptide variants by radial diffusion method. Inhibition zone is provided in millimeters for respective bacterial pathogens. Inhibition zone (mm)* Pseu- Escherichia Staphylococcus domonas Klebsiella Peptides coli aureus aeruginosa pneumoniae Chain300 — — — — Chain301 12 10  5 10 Chain302 12 12 10 — Chain303 12 10  4 — Chain304 14 16 16 11 Chain305 15 12 15 11 Chain306 12  8  9 — Chain307 19 20 20 17 Chain308 19 20 20 18 Chain309 11 10 10 11 Chain310 17 15 20 16 Chain311 13 14 18 13 Chain312 — — — — Chain313  8  7 14 — Gentamycin 22 24 24 22 Test concentration: Gentamycin - 5 μg; Peptides - 50 μg Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 25923), Klebsiella pneumoniae (ATCC 10031) and Pseudomonas aeruginosa (ATCC 27853) *Values in diameter including the wells.

TABLE 3a Minimum inhibitory concentration of different peptide variants tested against 4 bacterial pathogens. Hemolytic activity of the peptides was tested at 128 μg/ml and percent hemolysis is presented. Minimum inhibitory concentration (μg/ml) Escherichia Staphylococcus Klebsiella coli aureus pneumoniae Pseudomonas (ATCC (ATCC (ATCC aeruginosa % 25922) 25923) 10031) (ATCC 27853) Hemolysis* Chain100 >128 >128 >128 >128 0.4 Chain101 >128 >128 >128 >128 4.1 Chain102 >128 >128 >128 >128 5.0 Chain103 >128 >128 >128 >128 0.7 Chain104 8 32 16 0.25 0.5 Chain105 2 2 1 2 0.2 Chain106 >128 >128 >128 64 0.9 Chain107 64 >128 >128 >128 0.1 Chain108 >128 >128 >128 >128 0.5 Chain109 8 8 8 16 3.8 Gentamicin 1 0.25 0.25 0.25 — Tetracycline 8 2 2 32 — *Tested at 128 μg/ml

TABLE 3b Minimum inhibitory concentration of different peptide variants tested against 4 bacterial pathogens. Hemolytic activity of the peptides was tested at 128 μg/ml and percent hemolysis is presented. Minimum inhibitory concentration (μg/ml) Escherichia coli Staphylococcus Klebsiella Pseudomonas (ATCC aureus pneumoniae aeruginosa % 25922) (ATCC 25923) (ATCC 10031) (ATCC 27853) Hemolysis* Chain200 >128 >128 >128 >128 0.62 Chain201 2 4 8 8 0.56 Chain202 >128 >128 >128 1 0.56 Chain203 32 >128 >128 >128 0.46 Chain204 2 16 32 4 0.55 Chain205 64 >128 >128 >128 0.60 Chain206 16 >128 >128 >128 0.29 Chain207 >128 >128 >128 >128 0.33 Chain208 32 >128 >128 32 2.01 Chain209 64 >128 >128 >128 9.01 Chain210 >128 >128 >128 >128 8.61 Gentamycin 1 0.25 0.25 0.25 — tetracyclin 8 2 2 32 — *Tested at 128 μg/ml

TABLE 3c Minimum inhibitory concentration of different peptide variants tested against 4 bacterial pathogens. Hemolytic activity of the peptides was tested at 128 μg/ml and percent hemolysis is presented. Minimum inhibitory concentration (μg/ml) Escherichia coli Staphylococcus Klebsiella Pseudomonas (ATCC aureus pneumoniae aeruginosa % 25922) (ATCC 25923) (ATCC 10031) (ATCC 27853) Hemolysis* Chain300 >128 >128 >128 >128 6.81 Chain301 64 >128 >128 64 0.24 Chain302 >128 128 >128 16 0.44 Chain303 64 >128 >128 >128 0.22 Chain304 16 32 64 8 0.34 Chain305 128 64 64 16 0.43 Chain306 8 2 >128 64 0.04 Chain307 8 4 16 1 0.22 Chain308 1 4 4 2 0.32 Chain309 32 32 64 8 0.09 Chain310 4 8 16 1 3.69 Chain311 16 32 32 8 1.18 Chain312 >128 >128 >128 >128 4.87 Chain313 32 >128 >128 64 5.40 Gentamycin 1 0.25 0.25 0.25 — tetracyclin 8 2 2 32 — *Tested at 128 μg/ml

TABLE 4a Minimum inhibitory concentration of peptide variants as determined by microdilution method. Bacteria* Strains Chain104 Chain105 Chain109 Escherichia coli 1 4 1 16 2 4 4 4 3 4 1 4 4 4 1 4 5 4 2 4 Klebsiella pneumoniae 1 8 4 16 2 4 2 8 3 8 4 8 4 16 4 16 5 4 2 8 Pseudomonas aeruginosa 1 4 4 16 2 2 4 16 3 4 4 16 4 2 4 16 5 1 4 8 Serratia marcescens 1 >128 128 >128 2 >128 128 >128 3 >128 128 >128 4 >128 128 >128 5 128 128 64 Proteus mirabilis 1 >128 >128 >128 2 32 32 64 3 128 64 64 4 >128 >128 >128 5 >128 >128 >128 Enterobacter cloacae 1 4 2 4 2 4 2 8 3 8 2 8 4 4 2 8 5 2 1 4 Staphylococcus aureus 1 4 2 2 2 2 2 4 3 4 2 2 4 2 2 2 5 4 2 2 Streptococcus pneumoniae 1 4 4 16 2 2 2 8 3 1 2 2 4 4 4 8 5 1 2 8 Acinetobacter baumannii 1 16 4 — 2 8 4 — 3 8 4 — 4 4 2 — 5 8 4 — Acinetobacter johnsonii 1 8 4 — *The MIC values are determined by microdilution method using Muller Hinton broth-cation adjusted in presence of 0.02% BSA and 0.2% acetic acid.

TABLE 4b Minimum inhibitory concentration of peptide variants as determined by microdilution method. Bacteria* Strains Chain201 Chain204 Escherichia coli 1 16 8 2 1 1 3 1 1 4 1 1 5 1 1 Klebsiella 1 2 8 pneumoniae 2 2 4 3 4 16 4 4 4 5 2 2 Pseudomonas 1 4 4 aeruginosa 2 4 16 3 4 8 4 2 8 5 2 4 Serratia marcescens 1 64 >128 2 64 >128 3 64 128 4 64 >128 5 128 >128 Proteus mirabilis 1 >128 >128 2 32 32 3 64 64 4 >128 >128 5 >128 >128 Enterobacter cloacae 1 1 4 2 2 8 3 2 4 4 2 8 5 1 2 Staphylococcus 1 1 1 aureus 2 1 2 3 1 2 4 1 1 5 1 1 Streptococcus 1 8 4 pneumoniae 2 4 4 3 2 4 4 4 4 5 4 4 Acinetobacter 1 4 4 baumannii 2 4 4 3 4 4 4 4 4 5 4 4 Acinetobacter johnsonii *The MIC values are determined by microdilution method using Muller Hinton broth-cation adjusted in presence of 0.02% BSA and 0.2% acetic acid.

TABLE 4c Minimum inhibitory concentration of peptide variants as determined by microdilution method. Bacteria* Strains Chain304 Chain306 Chain307 Chain308 Chain309 Chain310 Chain311 Gentamicin Escherichia coli 1 1 1 4 1 0.5 4 2 0.5 2 16 2 4 0.5 32 32 2 0.5 3 16 2 4 1 16 16 1 1 4 32 2 2 1 32 16 0.5 1 5 32 2 4 1 16 16 1 1 Klebsiella 1 >128 128 8 4 128 64 8 2 pneumoniae 2 >128 >128 8 4 32 64 8 0.25 3 >128 >128 16 4 >128 128 4 2 4 >128 64 16 4 32 64 8 2 5 64 64 4 4 128 32 4 4 Pseudomonas 1 32 128 16 8 16 8 16 1 aeruginosa 2 64 >128 16 8 32 16 8 0.5 3 64 128 16 4 16 16 16 0.5 4 64 >128 8 4 32 8 8 0.5 5 16 128 8 4 8 4 4 0.25 Serratia 1 >128 >128 >128 128 >128 >128 >128 1 marcescens 2 >128 >128 >128 128 >128 >128 >128 2 3 >128 >128 128 64 >128 >128 >128 1 4 >128 >128 >128 >128 >128 >128 >128 1 5 >128 >128 >128 128 >128 >128 >128 1 Proteus mirabilis 1 >128 >128 >128 >128 >128 >128 >128 2 2 >128 >128 128 32 >128 >128 128 2 3 >128 >128 128 128 >128 >128 128 >128 4 >128 >128 >128 >128 >128 >128 >128 8 5 >128 >128 >128 >128 >128 >128 >128 >128 Enterobacter 1 64 64 4 2 >128 128 4 0.25 cloacae 2 64 64 8 2 128 64 4 0.25 3 128 32 4 2 64 16 4 0.25 4 128 16 4 2 64 8 4 0.25 5 32 16 4 2 32 16 2 0.25 Staphylococcus 1 32 16 2 1 8 8 1 0.5 aureus 2 32 32 2 2 16 16 1 0.5 3 16 32 2 1 8 8 1 0.5 4 16 16 2 2 8 8 1 0.5 5 16 8 2 2 8 4 1 0.5 Streptococcus 1 128 64 4 8 64 128 16 2 pneumoniae 2 128 64 4 4 64 128 8 2 3 128 64 4 8 64 128 16 2 4 128 128 2 2 64 128 4 2 5 64 64 2 4 64 64 8 1 Acinetobacter 1 — 16 — 4 — — — 0.5 baumannii 2 — 32 — 4 — — — 0.25 3 — 16 — 4 — — — 0.5 4 — 16 — 2 — — — 0.5 5 — 8 — 2 — — — 0.25 Acinetobacter 1 — 16 — 4 — — — 0.25 johnsonii *The MIC values are determined by microdilution method using Muller Hinton broth-cation adjusted in presence of 0.02% BSA and 0.2% acetic acid.

TABLE 5a Minimum inhibitory concentration of peptide variants tested against clinical yeast strains Fungi Strains Chain104D Chain105D Chain109D Candida albicans 1 8 32 128 2 8 16 128 3 8 32 128 4 8 32 128 5 8 32 128 C. glabrata 1 8 16 128 2 8 16 128 3 8 8 16 4 16 32 64 C. parapsilosis 1 4 8 128 2 4 8 128 3 4 8 128 4 2 4 8 C. quillermondiae 1 4 8 128

TABLE 5b Minimum inhibitory concentration of peptide variants tested against clinical yeast strains Fungi Strains Chain201D Chain204D Candida 1 16 8 albicans 2 8 8 3 8 8 4 16 8 5 8 8 C. glabrata 1 8 4 2 8 8 3 8 32 4 64 32 C. parapsilosis 1 8 4 2 8 4 3 8 8 4 8 8 C. quillermondiae 1 8 4

TABLE 5c Minimum inhibitory concentration of peptide variants tested against clinical yeast strains Fungi Strains Chain304D Chain306D Chain307D Chain308D Chain309D Chain310D Chain311D Amphotericin B Candida albicans 1 16 16 16 16 32 16 8 2 2 16 8 16 16 32 16 8 0.5 3 16 8 16 16 16 16 8 2 4 16 16 16 16 16 16 16 2 5 32 16 16 16 32 16 16 2 C. glabrata 1 16 8 8 16 32 16 16 4 2 16 8 16 16 64 16 16 4 3 8 16 8 16 4 128 8 2 4 64 32 16 16 128 128 64 4 C. parapsilosis 1 64 8 16 8 64 64 16 2 2 64 16 8 8 64 64 8 2 3 32 16 8 8 32 64 8 2 4 16 4 8 4 16 16 8 2 C. quillermondiae 1 16 4 4 4 8 8 4 2

TABLE 6 Minimum inhibitory concentration (MICs) of peptide variants against antibiotic resistant and sensitive strains of S. aureus and synergistic activity with Ertapenem. S. aureus COL + S. aureus S. aureus 4 μg/ml Compound RN4220 COL (MRSA) Ertapenem 104 >64 μg/ml >64 μg/ml 0.25 μg/ml 104 D 64 μg/ml 32 μg/ml 4 μg/ml 105 >64 μg/ml >64 μg/ml 0.5 μg/ml 105 D 16 μg/ml 8 μg/ml 2 μg/ml 201 64 μg/ml 64 μg/ml 0.5 μg/ml 201 D 2 μg/ml 2 μg/ml 1 μg/ml 308 >64 μg/ml >64 μg/ml 0.5 μg/ml 308 D 4 μg/ml 4 μg/ml 1 μg/ml 310 >64 μg/ml >64 μg/ml 0.06 μg/ml 310 D >64 μg/ml >64 μg/ml <0.03 μg/ml *D—D-Amino acids.

REFERENCES

-   Andersen A. S., Sandvang D., Schnorr K. M., Kruse T., Neve S.,     Joergensen B., Karlsmark T., and Krogfelt K. A. (2010) A novel     approach to the antimicrobial activity of maggot debridement     therapy. J Antimicrob Chemother 65, 1646-1654. -   Pirttilá, A. M., Kämäräinen, T., Hirsikorpi, M., Jaakola, L., and     Hohtola, A. (2001). DNA isolation methods for medicinal and aromatic     plants. Plant molecular biology report 19, a-f.

Schmidtchen, A., Rigstad, L., Kasetty, G., Mizuno, H., Rutlands M. W. and Malsten, M. (2011) Membrane selectivity by W-tagging of antimicrobial peptides. Biochem Biophys Acta 1808, 1081-1891.

Van Lith, M., Karala, A. R., Bown, D., Gatehouse, J. A., Ruddock, L. W., Saunders, P. T., and Benham, A. M. (2007). A developmentally regulated chaperone complex for the endoplasmic reticulum of male haploid germ cells. Mol. Biol. Cell 18, 2795-2804.

-   Wang, G. S., Li, X., and Wang, Z. (2009) APD2: The updated     antimicrobial peptide database and its application in peptide     design. Nucleic Acids Res. 37, D933-D937. 

1. An antimicrobial peptide or a variant thereof comprising SEQ ID NO: 6 or having at least 37%, preferably at least 50% identity to SEQ ID NO:
 6. 2. The peptide of claim 1 wherein said peptide is modified in order to increase antimicrobial activity.
 3. The peptide of claim 1 wherein said peptide is modified with one or more of W, R, K, L, and I-substitutions, preferably with one or more of W and R-substitutions.
 4. The peptide of claim 1 comprising one or more substitutions or deletions in SEQ ID NO: 6 selected from the group consisting of a. Y1I/R/W/K b. D2I/L/W/R d. G4R/W e. F5W/R f. G6R/W/L h. F8R i. K9R j. K10R k. M11L/R/W/K.
 5. The peptide of claim 1 comprising any of SEQ ID NOs: 6 and 55 to 67, preferably 55 to
 41. 6. The peptide of claim 6 comprising any of SEQ ID NOs: 55, 58, 59 and 61 to
 65. 7. The peptide according to claim 1, having an activity against fungi or yeast.
 8. The peptide according to claim 1, having an activity against bacteria.
 9. A peptide as defined in claim 1 for use in therapy, particularly for use as an antimicrobial agent.
 10. A method of killing or inhibiting growth of microbes, comprising a step of treating said microbes with a peptide according claim
 1. 11. The method according to claim 10, wherein the peptide exhibits an activity against bacteria or fungi or both bacteria and fungi.
 12. Use of the peptide according to claim 1 as a medicament, feed additive, preservative or surfactant. 